Mice receiving i.p. vaccinia virus (VV) infection after recovery from lymphocytic choriomeningitis virus (LCMV) infection become clinically ill, a condition not caused by either virus alone. Histological examination of the sick mice reveals no abnormalities except for an extensive macrophage and lymphocyte infiltration of adipose tissue and for large necrotic areas in pelvic, mesenteric, and perirenal fat. This may be a model for Weber-Christian disease as well as a model for unique immunopathology resulting from sequential infections with two antigenically unrelated viruses. Experiments are designed to examine viral replication in adipocytes and to determine if latent viruses are activated by the infection sequence. The local immune response in the peritoneum will be analyzed. A protocol for adoptive transfer of leukocytes into cyclophosphamide-treated mice is outlined to examine the nature of the effector cell as well as target cell requirements. Primary adipocyte cultures will be examined for susceptibility to cytotoxic T cells. Adipocytes will be exposed to IFN in vivo and in vitro to determine if it renders them more sensitive to CTL by examining expression of histocompatibility antigens.